1. Field of the Invention
The present invention relates generally to apparatuses and methods of forming a film of liquid applied on a substrate and particularly to apparatuses dropping a liquid to be applied on an upper surface of a substrate held substantially horizontally and rotated as controlled to disperse the liquid in the form of a film to form a film to be applied and methods of forming such film.
2. Description of the Background Art
In fabricating a semiconductor device a photolithography process is performed including, e.g., the step of applying resist liquid serving as a liquid to be applied on a semiconductor wafer (hereinafter simply referred to as a “wafer”) serving as a substrate to be processed to form a film of the resist, the step of exposing the film of the resist to form the film of the resist in a predetermined pattern, the step of heating the exposed film of the resist to promote a chemical reaction therein (i.e., the step of post-exposure baking), the step of developing the exposed film of the resist, and the like in order to form a predetermined pattern of the resist on the wafer.
Of the series of process steps, the step of applying the resist is performed for example in a well-known apparatus employing spin-coating to form an applied film, as indicated in Japanese Patent Laying-Open No. 07-320999. FIG. 7 shows in configuration the apparatus indicated in the document such that it is partially simplified. FIG. 7 shows an apparatus 200 forming an applied film. More specifically, a spin chuck 201 with a wafer W placed and thus fixed thereon is rotated and a solvent (thinner or the like) serving as a solvent for resist liquid is initially dropped at a center of an upper surface of wafer W from a solvent feeding mechanism 202 through a nozzle 203 and thus dispersed, and the resist liquid is then dropped by a resist feeding mechanism 204 through a nozzle 205. The dropped resist liquid is dispersed from the center of the wafer toward the perimeter of the wafer spirally by the rotational force of wafer W and the centrifugal force and thus applied on the wafer.
When spin-coating is employed to perform an application process, as indicated in the document, the resist liquid dispersed on wafer W that is excessive is spun away from wafer W by the force of rotation of wafer W. Of the resist liquid spun and thus scattered away, a portion is accommodated in an application cup 206 and a portion forms an atmosphere in the form of a mist around wafer W. Accordingly the configuration indicated in the document has an exhaust port 207 under application cup 206 to aspirate therethrough the mist formed around wafer W.
The configuration with application cup 206 having an upper portion open and exhaust port 207 located under wafer W, as shown in FIG. 7, however, forms an exhaust flow path which affects the film to be uneven in thickness, and this is a technological issue to be addressed.
More specifically, when the mist formed around wafer W is aspirated through exhaust port 207, as shown in the figure, the mist is aspirated together with external air present above wafer W. This forms a downward exhaust flow path. As a result, wafer W receives larger wind pressure at the perimeter than at the center. The perimeter is thus dried faster and on the dried resist the resist liquid is further applied resulting in wafer W having a film thereon larger in thickness at the perimeter than at the center.
Furthermore, as shown in FIG. 7, between application cup 206 and wafer W a large gap G is formed. As such, the mist also leaks and thus moves to above wafer W. Accordingly, aspirating through exhaust port 207 all of the mist having moved to above wafer W requires powerful aspiration, which is also an issue to be addressed.
Furthermore, measuring an amount of exhaust in the configuration of FIG. 7 requires that an anemometer, a flowmeter and/or the like be arranged in the exhaust flow path downstream, i.e., at exhaust port 207 or the like. In that case, however, the measuring instrument is contaminated by the mist and cannot measure the amount of exhaust precisely.